which should reduce the input files to 1600 pixels wide, saving the file with the original name appended with "small". This is seriously untested, ymmv. Besides, you're probably using Linux - if so, post back, and someone can help there. Ditto if you're looking for a Python solution.

Edited: added parameter to create ESRI world file. Note that this solution doesn't specify the output format, so it's a GeoTiff by default